The present invention relates to molded thermoplastic articles and more particularly to elongate molded thermoplastic articles which have been strenghtened to prevent distortion when the articles are subjected to thermal stresses, e.g. when the articles cool in the mold and/or during usage.
A wide variety of products can be molded from thermoplastic material. When the articles are small or dimensionally the same in length and width, relatively uniform shrinkage of the thermoplastic material occurs when the article is cooling in the mold. For elongate objects (that is objects having a length to width ratio of greater than about 4:1), molded thermoplastic articles often can become distorted when the article cools in the mold and the thermoplastic material shrinks. This is particularly true when, for example, parking blocks are being formed from thermoplastic material. Parking blocks can range in length from about three feet to eight feet or greater with widths of much less than one foot. When such molded articles cool in the mold, the parking blocks have a tendency to bend and twist.
The difference in modulus between plastic and metal militate against use of rebar or similar reinforcement in such elongate molded articles. Thus, the manufacturer is faced with the difficult task of maintaining the shape and dimensional tolerances of the molded article without adversely impacting weight and cost considerations.